Serum inhibin B levels in community-dwelling elderly men

BACKGROUND AND OBJECTIVE Ageing in men is accompanied by a decline of Leydi g cell function, with a 50% decrease of the population means for serum free testosterone between age 25 and 75 years. Information on Sertoli cell func tion and spermatogenesis in the elderly is scarce. Studies on seminal param eters in ageing men have suggested that spermatogenesis may be fairly well maintained in the elderly, but they included mostly selected subjects and o nly few men over 60 years. More systematic studies are lacking. The aim of the present study was to assess serum inhibin B levels in elderly men as an index of global Sertoli cell function and spermatogenic activity. SUBJECTS AND MEASUREMENTS Specific immunoassays were used to determine seru m levels of inhibin B, gonadotrophins, testosterone and oestradiol in blood obtained between 0800 and 1000 h. from 189 ambulatory, community-dwelling elderly men (age: 70-85 years) and, for comparison, from 51 middle-aged (35 -54 years) and 50 young (< 35 years) controls. RESULTS All age groups combined, serum inhibin B was only weakly negatively correlated to age (Spearman correlation coefficient: - 0.17; P<0.01) and m ore strongly to serum FSH (- 0.52; P<0.001). In a multiple regression analy sis serum FSH, but not age or serum free testosterone, emerged as an indepe ndent determinant of serum inhibin B levels. An age-related decline of medi an inhibin B levels in the study population was essentially limited to the younger age groups, with stable levels between age 35 and 79 years, and onl y a modest further decrease thereafter. There was a progressive age-related increase of serum FSH across age groups with, consequently, a marked decre ase of the serum inhibin B:FSH ratio. The prevalence of men presenting with low serum inhibin B (below 10th percentile for inhibin B levels in men <35 years), indicative of deficient Sertoli cell function and spermatogenesis, increased most strikingly between men < 35 years and those 35-54 years, wh ich contrasts with the more progressive increase at an older age of the pre valence of low serum (free) testosterone. CONCLUSION Global testicular Sertoli cell function and spermatogenic activi ty, as assessed indirectly through serum inhibin B levels, appear to be wel l maintained in ambulatory elderly men, albeit there are age-related altera tions at the level of the Sertoli cells as indicated by a progressive incre ase of testicular drive by pituitary FSH.